Cream the cream cheese and margarine together in small mixer bowl. Add vanilla. Beat in confectioners’ sugar until frosting is smooth and well blended. Spread evenly over the bars.

These bars freeze very well. If the pan doesn’t have a lid, place bars in freezer uncovered just until frozen, then cover with aluminum foil. When defrosting, remove aluminum foil as soon as you take them out of the freezer so the frosting doesn’t stick to the foil.